1. Field of the Invention
The present invention relates to a CCD (charge coupled device) solid-state imaging device and imaging apparatus having a charge transfer path (transfer register) whose output end is branched into two parallel parts, and more particularly to a two-branch outputting solid-state imaging device and imaging apparatus that the signal charges distributed to the branch output ends are converted into voltage signals and output by separate amplifiers.
2. Description of Related Art
The CCD solid-state imaging device recently has pixels increasing in the number, e.g. having several million pixels, along with the progress of semiconductor micro-fabrication techniques. This requires an increased frequency to drive the horizontal transfer path from which a signal is to be read, thus incurring an issue of a waveform disturbance in the voltage signal output from the output amplifier.
In such a situation, there is developed an art that the horizontal transfer path is branched parallel at its output end to drive the horizontal transfer path at higher frequency so that the signal charges, sequentially transferred over the horizontal transfer path, can be distributed in order at a distributor (branching part) into branch transfer paths, thereby providing the drive frequency to the branch transfer path lower than the drive frequency to the horizontal drive line (e.g. JP-A-5-308575, Japanese Patent No. 2,949,861 and Japanese Patent No. 2,624,138).
The technique described in JP-A-5-308575 is structured that the output end of the horizontal transfer path is branched into three parts so that signal charges R (red), G (green) and B (blue) can be respectively distributed to the branch transfer paths where those are transferred and output. Thus, the drive frequency to the branch transfer paths is provided one-thirds of the drive frequency to the horizontal transfer path.
However, for the solid-state imaging having several millions of pixels or more allowing for taking an image with definition, e.g. high vision of image quality, there is a need to drive the horizontal transfer path at considerably high frequency. There is a difficulty in well distributing the signal charges at the distributor part into three lines while maintaining the transfer efficiency high (i.e. with no or less remaining charge).
Japanese Patent No. 2,949,861 and Japanese Patent No. 2,624,138 describe the techniques that propose two-branch outputting solid-state imaging devices. The two-branch outputting type is easy to distribute the signal charges to branch lines as compared to that in the three-branch outputting type. Besides, it is advantageous in that the drive frequency to the horizontal transfer path is satisfactorily double the drive frequency to the branch transfer paths.
However, Japanese Patent No. 2,949,861 and Japanese Patent No. 2,624,138 fail to describe the transfer of color-image signal charges. In the two-branch outputting solid-state imaging device, unless charges are distributed with efficiency at the branching part, the residual portion of signal charge distributed preceding in stage, e.g. red, is mixed in the next stage of signal charge, e.g. green, thus raising a problem of image deterioration in the image taken.
The two-branch outputting solid-state imaging device has an advantage that data rate can be increased over the horizontal transfer path because of the capability of lowering the post-branch drive frequency down to a half. However, unless charge distribution is effected with efficiency, a color mixture results to problematically deteriorate the quality of image.